Data transfer networks include network elements such as, for example, routers, switches, and terminal devices which communicate with each other via data transfer links between the network elements. In order to provide a sufficient quality of service, data transfer networks should be able to operate also in situations in which a failure takes place in a network element or in data transfer links to or from the network element. For achieving secure and reliable operation, important active network elements of data transfer networks are secured with respective backup network elements. The backup network element is activated to perform at least part of the tasks of the respective active network element as a consequence of an event representing a deliberate network management order or a failure in the active network element and/or in data transfer links to or from the active network element. Therefore, this arrangement provides protection against failures in the active network element and in data transfer links to or from the active network element. Traditionally, the backup network element is configured to operate in the prevailing circumstances after an event which causes a need to activate the backup network element has already occurred. In a case of a failure event, this traditional way provides, however, only a slow traffic restoration.
Publication US2007263532 discloses an arrangement where a SONET (Synchronous Optical NETwork) terminated by routers includes working data transfer paths and backup data transfer paths. The routers pre-configure into their link state data bases the links of both the working and backup data transfer paths. However, the links involved in the backup data transfer paths are given higher costs. Thus, in normal circumstances, the routers select only the links of the working data transfer path. If there is a failure in a link of a working data transfer path, the arrangement provides a switchover to activate the corresponding backup data transfer path. This is accomplished by changing the relative costs of the working and backup links involved, so that the routers select the backup links for their routing tables. This arrangement is designed for protecting a data transfer path from a first router to a second router with a backup data transfer path that is also from the first router to the second router. This arrangement is not, however, at least directly suitable for protecting the above-mentioned first router or the second router. This arrangement does not work at all if one of the first and second routers gets out of the service due to e.g. problems in the electric power supply or some other reason. Furthermore, this arrangement is based on the traditional principle that configuration is changed only after a failure has already taken place, i.e. the changing of the relative costs of the working and backup links is accomplished only after the failure has taken place. In many situations, this traditional principle provides only a slow traffic restoration.